1. Field of the Invention
The present invention relates to a reflective liquid crystal display device and a manufacturing method thereof, and more particularly, to a reflective liquid crystal display device with a black alignment layer and a manufacturing method thereof.
2. Description of the Prior Art
Compact designs and low power consumptions may be realized in reflective liquid crystal display devices because backlight units are not required for the reflective liquid crystal display. Among all kinds of liquid crystals, the cholesteric liquid crystal is suitable for the low power consumption reflective liquid crystal display device because the cholesteric liquid crystal may be employed to selectively reflect light within a wavelength range and kept in a bistable state when applied voltages are removed.
For analyzing the display mechanism of the cholesteric liquid crystal display device, please refer to FIGS. 1A-1C. FIGS. 1A-1C are schematic diagrams illustrating different display modes of the reflective cholesteric liquid crystal display device according to a prior art. FIG. 1A is a schematic diagram illustrating the reflective cholesteric liquid crystal display device in a planar state without voltages applied. FIG. 1B is a schematic diagram illustrating the reflective cholesteric liquid crystal display device in a homeotropic state with voltages applied. FIG. 1C is a schematic diagram illustrating the reflective cholesteric liquid crystal display device in a focal conic state when the applied voltages are removed. As shown in FIG. 1A, a plurality of cholesteric liquid crystal molecules 14M are disposed on a substrate 301 and disposed between a first pixel electrode 161 and a second pixel electrode 162. When there are no voltages applied to the first pixel electrode 161 and the second pixel electrode 162, the cholesteric liquid crystal molecules 14M are preserved in the planar state. The cholesteric liquid crystal molecules 14M may selectively reflect light within a wavelength range and allow light beyond the wavelength range to pass through in the planar state. As shown in FIG. 1A, an incident light C includes an incident light A and an incident light B. A wavelength range of the incident light A is different from a wavelength range of the incident light B. A transmissive light AT may be generated by the incident light A passing through the cholesteric liquid crystal molecules 14M. A reflected light BR may be generated by the incident light B reflected by the cholesteric liquid crystal molecules 14M, and then a bright state display effect is presented within the wavelength range of the reflected light BR. When a voltage bias, which is capable of driving the cholesteric liquid crystal molecules 14M into the homeotropic state, is applied between the first pixel electrode 161 and the second pixel electrode 162, as shown in FIG. 1B, the voltage bias may drive the cholesteric liquid crystal molecules into the homeotropic state, and a dark state display effect is presented because the incident light C completely passes though the cholesteric liquid crystal molecules 14M to form a transmissive light CT. As shown in FIG. 1C, when the voltage bias between the first pixel electrode 161 and the second pixel electrode 162 is removed, the cholesteric liquid crystal molecules 14M are driven into the focal conic state, and the dark state display effect is still presented because the incident light C may be scattered by the cholesteric liquid crystal molecules 14M to form scattered lights CD. However, when the substrate 301 in the reflective cholesteric liquid crystal display device is an array substrate with metal patterns, the substrate 301 may reflect light. As shown in FIGS. 1A-1C, the transmissive light AT, the transmissive light CT, and the scattered light CD may be reflected by the substrate 301 and then a reflected light AR, a reflected light CR, and a reflected light DR are generated. The reflected light AR may interfere with the reflected light BR in the bright state display mode, and then affects the color purity of the reflective cholesteric liquid crystal display device. The reflected light CR and the reflected light DR may induce light leakage issue in the dark state display mode, and then affects the contrast ratio of the reflective cholesteric liquid crystal display device.
In conventional reflective cholesteric liquid crystal display devices, a black absorption layer is generally disposed on a surface of the substrate to absorb the transmissive light and the scattered light passing through the cholesteric liquid crystal molecules and reduce the influence on the color purity and the contrast ratio of the reflective cholesteric liquid crystal display device. However, some area of the substrate may not be covered by the black absorption layer for positioning function in subsequent module process. Therefore, in the conventional related art, a process for forming the black absorption layer and an additional process for patterning the black absorption layer are both required. The complexity of the manufacturing process may then increase and affect the yield performance and the cost of the reflective cholesteric liquid crystal display device.